JPH0526894A - Acceleration sensor with self-diagnostic circuit - Google Patents

Abstract

PURPOSE:To check the function of an acceleration sensor unit by itself and also carry out the self-diagnosis of its electronic circuit and the power supply circuit thereof. CONSTITUTION:A self-oscillation circuit 4 is connected to a self-excited electrode 2A of the unpolarized part of an acceleration sensor unit 3 having the polarized part and the unpolarized part, and an amplifier circuit 5 to amplify an oscillating signal S1 output from a detecting electrode 2B of the polarized part of the sensor unit 3 and a collision signal S2 generating in the collision time of a motorcar, etc., is connected to the electrode 2B. An offset diagnosis circuit 6 to detect an offset signal S3 applied to the amplifier circuit 5 and output a diagnostic signal S4, and a self-excited signal diagnostic circuit 7 to amplify and detect the said signal S1 and output a oscillating diagnostic signal S5 are connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor which is applied to an airbag system or the like which operates when a vehicle crashes to reduce the impact on the driver, and more specifically, the acceleration sensor senses the impact caused by the collision. When the set value is exceeded, the bag built into the steering wheel pad is deployed,
The present invention relates to an acceleration sensor that can be used to reduce the impact on a driver, and particularly to an acceleration sensor with a self-diagnosis circuit that can perform self-diagnosis.

[0002]

2. Description of the Related Art Conventionally, electrodes are provided on both sides of a piezoelectric body and are composed of an acceleration sensor unit which outputs a collision signal when a vehicle collides, and an amplification circuit which amplifies the collision signal output from this unit.

In such a conventional example, when a vehicle collides, the impact is detected by the acceleration sensor unit, and the impact signal output from the unit is amplified by the amplification circuit and used for the operation of the airbag system.

[0004]

However, in the above-mentioned conventional example, even if a highly reliable acceleration sensor unit is used, it is necessary to check the function of the sensor itself because it affects human life. An object of the present invention is to provide an acceleration sensor with a self-diagnosis circuit, which can not only check the function of the acceleration sensor unit itself but also self-diagnose its electronic circuit and its power supply-related circuit.

[0005]

In order to solve the above-mentioned problems and achieve the above-mentioned object, the sensor of the present invention has a piezoelectric body 1 having a polarized portion and a non-polarized portion, and is self-excited provided in the non-polarized portion. The oscillation signal S is applied to the acceleration sensor unit 3 having the electrode 2A and the detection electrode 2B provided in the polarized portion, and the self-excited electrode 2A.
A self-excited oscillation circuit 4 for applying 0, and an amplification circuit 5 for amplifying an acceleration signal S2 generated at the time of a vibration or collision of a vehicle output from the detection electrode 2B and superimposing an offset signal S3.
An offset diagnostic circuit 6 for detecting the offset signal S3 and outputting an offset diagnostic signal S4 corresponding to the offset signal; and an oscillation signal S1 generated at the detection electrode 2B in response to the oscillation signal S0. The self-excited signal diagnostic circuit 7 outputs the oscillation diagnostic signal S5 corresponding to.

[0006]

When the oscillation signal S0 is applied from the self-excited oscillation circuit 4 to the self-excited electrode 2A of the acceleration sensor unit 3, the detection electrode 2 is detected.
An oscillation signal S1 proportional to the oscillation signal S0 is induced in B by capacitance coupling, and it can be diagnosed that the sensor unit 3 is operating normally while the oscillation signal S1 is detected. The oscillation signal S1 is impedance-converted by the amplifier circuit 5 and input to the self-excited signal diagnostic circuit 7.

The set DC offset signal S3 applied to the amplifier circuit 5 is amplified and output as a DC offset output voltage when the acceleration is 0 G, and when it is within the voltage range set by the offset diagnosis circuit 6, the offset diagnosis is performed. Since the signal S4 is in the "H" state, it can be diagnosed that the amplifier circuit 5 and the power supply related circuit of each circuit section are normal.

The signal S1 is detected by the self-excited signal diagnostic circuit 7, and the oscillation diagnostic signal S corresponding to the detected signal S1 is detected.
When 5 is output from the circuit 7, it can be diagnosed that the self-oscillation circuit 4 and the sensor unit 3 are normal.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a connection diagram showing the structure of one embodiment of the sensor of the present invention, FIG. 2 is a front view showing an example of an acceleration sensor unit according to the present invention, FIG. 3 is its rear view, and FIG. Is. In FIG. 1, the acceleration sensor unit 3 partially polarizes the piezoelectric film body to form the piezoelectric body 1, and the self-exciting electrode 2A is formed in a portion having no polarization, and the detection electrode 2B is formed in a portion having polarization and piezoelectricity. And a common electrode 2C (see FIG. 2), an intermediate electrode 2D is provided on the other surface (see FIG. 3), and a backing material 9 and a support frame 10 are attached to the intermediate electrode 2D side (FIG. 4). reference).

When the detection electrode 2B and the common electrode 2C are provided on one surface of the piezoelectric body 1 and the intermediate electrode 2D is provided on the other surface to form the equivalent circuit of FIG. Also, the pyroelectric output is offset, and the output change due to the temperature change is prevented.

Reference numeral 4 denotes a self-excited oscillation circuit for applying an oscillation signal S0 having a frequency of, for example, 5 kHz to the self-excited electrode 2A of the sensor unit 3. Reference numeral 21 denotes a switch for constant monitoring and timing monitoring, which is closed during constant monitoring. It is a switch that is closed for a desired time during timing monitoring.

Reference numeral 5 denotes a signal S1 proportional to the oscillation signal S0 output from the detection electrode 2B of the sensor unit 3, vehicle vibration,
It is an amplifier circuit that amplifies the acceleration signal S2 generated at the time of collision and superimposes the set DC offset signal S3. The amplifier circuit 5 includes an impedance converter 11 that receives the oscillation signal S1 and the acceleration signal S2, a high-pass filter 12 that receives the output of the impedance converter 11, an output of the filter 12 and an offset voltage generated by an offset signal generator 20. It is composed of an amplifying section 13 that receives S3 and a low-pass filter 14 that receives the output of the amplifying section 13. Oscillation signal S1 amplified together with acceleration signal S2
Is removed by the low-pass filter 14 and the acceleration signal S2 and the offset voltage S3 are output.

Reference numeral 6 is an offset diagnostic circuit which receives the amplified signal S2 and the offset voltage S3 and outputs a signal S4 corresponding to the output offset signal voltage. The offset diagnosis circuit 6 compares the signals S2 and S3 output from the low pass filter 14 with a set voltage, and outputs a normal output when S2 + S3 is normal and within the set voltage, and outputs 0 V when S2 + S3 is abnormal and exceeds the set voltage. One comparator circuit 1
It consists of 5. In addition, even if the sensor unit 3 and the amplifier circuit 5 are normal, the acceleration signal S2 exceeds the set voltage and the comparator circuit 15 outputs 0 V for a short time at the time of a collision in which the vibration of the vehicle is large.

Reference numeral 7 denotes a self-excited signal diagnostic circuit that detects the oscillation signal S1 of the signals S1 and S2 output from the impedance converter 11 and outputs an oscillation diagnostic signal S5 corresponding to the detection signal S1. The self-excited signal diagnostic circuit 7 includes a high-pass filter 17 that detects the oscillation signal S1 of the signals S1 and S2 output from the impedance converter 11, an amplifier 18 that amplifies the output of the filter 17, and an amplifier 18 of the amplifier 18. Square wave oscillation diagnostic signal S depending on output voltage
The comparator circuit 19 outputs the value 5 to the integrator 16.

Reference numeral 8 is an abnormal signal diagnostic circuit which compares the outputs of the offset diagnostic circuit 6 and the self-excited signal diagnostic circuit 7 with a set voltage, and outputs a self-diagnostic signal S7 indicating that normal operation is performed within a predetermined output range. Integrator 16 and comparator circuit 22
Consists of.

The operation of this embodiment having the above-described structure is shown in FIG.
Will be explained. FIG. 6 is a waveform diagram for explaining the operation of each part of the electronic circuit of the present invention. The switch 21 is kept closed during constant monitoring, and the switch 21 is kept closed during a desired time during timing monitoring. When an oscillation signal S0 (see (a) of FIG. 6) is applied to the self-excited electrode 2A of the acceleration sensor unit 3 from the self-excited oscillation circuit 4, a signal proportional to the oscillation signal S0 is attracted to the detection electrode 2B by capacitance coupling. While the oscillation signal S1 is being detected, it can be diagnosed that the sensor unit 3 is operating normally. Further, when the oscillation signal S1 cannot be detected, it can be understood that the sensor unit 3 is abnormal, for example, peeling of the electrode, disconnection of the connecting portion, etc. (see (b) and (c) of FIG. 6).

The oscillation signal S1 is input to the impedance converter 11 of the amplifier circuit 5. The impedance converter 11 matches the output impedance of the detection electrode 2B of the sensor unit 3 with the input impedance of the high pass filters 12 and 17, and outputs the oscillation signal S1 and the acceleration signal S2 to the high pass filters 12 and 17 without loss. Play a role. The oscillation signal S1 passes through the high-pass filters 12 and 17 and is input to the amplifiers 13 and 18 and amplified. Here, the high pass filter 12 is installed for the purpose of removing the DC output of the impedance converter 11, and the cutoff frequency is set to a low frequency (about 1 Hz or less).
Further, the high-pass filter 17 of the self-excited signal diagnostic circuit 7 has a cutoff frequency set near the oscillation signal frequency, and the acceleration signal S2 having a relatively low frequency is removed.

Amplified oscillation signal S1 and acceleration signal S2
And the DC output offset voltage S3 when the acceleration is 0 G (see FIG.
(See (d)) is input to the low-pass filter 14. The oscillation signal S1 is removed by the filter 14, and the acceleration signal S2 and the DC output offset voltage S3 (see (e) in FIG. 6) are input to the comparator circuit 15 of the offset diagnosis circuit 6 and compared with the two set voltages. As a result, the offset diagnosis signal S4 (see (f) in FIG. 6) is output. When an abnormality occurs in the amplifier circuit 5 or the like and S2 + S3 exceeds the set voltage, the offset diagnosis signal S4 becomes 0V.

On the other hand, the oscillation signal S1 input to the high pass filter 17 of the self-excited signal diagnostic circuit 7 is
Through the oscillation signal S1 and is input to the amplification unit 18 and amplified. The amplified oscillation signal S1 is input to the comparator circuit 19 and compared with the set voltage, and a square wave oscillation diagnostic signal S5 of a higher frequency than the circuit 19 (see (c) of FIG. 6).
Is output.

Comparator circuit 1 of self-excited signal diagnostic circuit 7
When the square wave oscillation diagnostic signal S5 is output from 9, the self-excited oscillation circuit 4, the impedance changing section 11 of the amplifier circuit 5, the self-excited state of the sensor unit 3, the detection electrode 2A,
It shows that the state of 2B and the connection state are normal,
When the signal S5 is not output, any of the sensor unit 3, the self-excited oscillation circuit 4, and the impedance conversion unit 11 of the amplification circuit 5 is abnormal.

Offset diagnostic signal S4, oscillation diagnostic signal S
5 is input to the integrator 16 of the abnormality diagnosis circuit 8, outputs a predetermined DC voltage signal S6 (see (g) of FIG. 6), is input to the comparator circuit 22, is compared with the set voltage, and is self-diagnostic signal S7. Is output. Offset diagnostic signal S4
When the oscillation diagnosis signal S5 is normal, both are power supply voltage values, the integrator output signal S6 becomes a value close to the power supply voltage, and the self-diagnosis signal S7 outputs 0 V, indicating that normal operation is in progress. Further, when the sensor unit 3, the amplifier circuit 5, etc. are abnormal, either or both of the oscillation diagnosis signal S5 and the offset diagnosis signal S4 become 0V, and the integrator output signal S6.
Also becomes 0V. As a result, the self-diagnosis signal S7 outputs an open state, indicating that an abnormality has occurred (see (h) in FIG. 6).

Thus, according to this embodiment, the self-exciting electrode 2A, the detecting electrode 2B and the common electrode 2C are provided on one surface of the piezoelectric body 1.
By using the highly reliable acceleration sensor unit 3 in which the intermediate electrode 2D is provided on the other surface and the backing material 9 and the support frame 10 are attached to the intermediate electrode 2D side, the acceleration can be detected more reliably and the acceleration can be detected. The sensor unit 3 can be diagnosed by inputting the oscillation signal S0 into the self-excited electrode 2A of the sensor unit 3 and outputting the oscillation signal from the detection electrode 2B.

Further, by connecting the amplification circuit 5 to the detection electrode 2B of the sensor unit 3 and connecting the offset diagnosis circuit 6 and the self-excited signal diagnosis circuit 7 to the amplification circuit 5, not only the sensor unit 3 but also the self-excited oscillation. The circuit 4, the power supply related circuit of each circuit, and the amplifier circuit 5 can be diagnosed.

[0024]

As is apparent from the above description, according to the present invention, not only the function of the acceleration sensor unit 3 itself can be checked but also its electronic circuits 4, 5, 5.
It is possible to diagnose abnormalities in circuits 6 and 7 and their power supply related circuits.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a configuration of an embodiment of a sensor of the present invention.

FIG. 2 is a front view showing an example of an acceleration sensor unit according to the present invention.

FIG. 3 is a rear view of the same.

FIG. 4 is a sectional view of the same.

FIG. 5 is an equivalent circuit diagram of the same.

FIG. 6 is a waveform diagram for explaining the operation of each part of the electronic circuit of the present invention.

[Explanation of symbols]

1 Piezoelectric body 2A self-excited electrode 2B detection electrode 2C common electrode 2D intermediate electrode 3 Acceleration sensor unit 4 Self-excited oscillation circuit 5 amplifier circuit 6 Offset diagnosis circuit 7 Self-excited signal diagnostic circuit 8 Abnormality diagnosis circuit 10 Support frame 11 Impedance converter 12 High-pass filter 13 Amplifier 14 Low-pass filter 15 Comparator circuit 16 integrator 17 High-pass filter 18 Amplifier 19 Comparator circuit 20 Offset signal generator S0 oscillation signal S1 oscillation signal proportional signal S2 acceleration signal S3 Offset signal (voltage) S4 Offset diagnostic signal S5 oscillation diagnostic signal S6 integrator output signal S7 self-diagnosis signal

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akira Gokura             2-5-3 Marunouchi 2-chome, Chiyoda-ku, Tokyo             Ryo Yuka Co., Ltd. Electronic Product Development Center

Claims (4)

[Claims] 1. An acceleration sensor unit having a piezoelectric body (1) having a polarized portion and an unpolarized portion, and having a self-excited electrode (2A) provided on the unpolarized portion and a detection electrode (2B) provided on the polarized portion. (3), the self-excited oscillation circuit (4) that applies the oscillation signal (S0) to the self-excited electrode (2A), and the acceleration signal (S2 that is output from the detection electrode (2B) when the vehicle vibrates or collides. ) And an offset signal (S
3) is superimposed on the amplification circuit (5) and the offset signal (S
Offset diagnosis circuit (6) for detecting 3) and outputting an offset diagnosis signal (S4) corresponding to the offset signal
And an oscillation signal (S1) generated in the detection electrode (2B) corresponding to the oscillation signal (S0) is detected, and this oscillation signal (S1) is detected.
An acceleration sensor with a self-diagnosis circuit, which comprises a self-excited signal diagnosis circuit (7) that outputs an oscillation diagnosis signal (S5) corresponding to. 2. The offset diagnostic circuit (6) and the self-excited signal diagnostic circuit (7) are input, and when the output is within a predetermined output range, a self-diagnostic signal (S7) indicating normal operation is output. The acceleration sensor with a self-diagnosis circuit according to claim 1, further comprising an abnormality diagnosis circuit (8). 3. The acceleration sensor with a self-diagnosis circuit according to claim 1, wherein the acceleration sensor unit (3) has a support frame (10) attached to the side of the intermediate electrode (2D). 4. The amplifier circuit 5 includes an impedance converter (11) for inputting an oscillation signal (S1) and an acceleration signal (S2).
A high-pass filter (12) for inputting the output of the impedance converter (11), an amplifier (13) for inputting the output of the filter (12) and a DC offset signal setting output (S3), and the amplifier The low-pass filter (14) inputs the output of (13), and the offset diagnosis circuit (6) includes a comparator circuit (15) that compares the output of the low-pass filter (14) with a set voltage. The self-excited signal diagnostic circuit (7) includes a high-pass filter (1) to which the output of the impedance converter (11) is input.
7), an amplification section (18) for amplifying the output of the filter (17), and a comparator circuit (19) for comparing the output of the amplification section (18) with a set voltage to output an oscillation diagnosis signal (S5). The acceleration sensor with a self-diagnosis circuit according to claim 1, wherein